In chemical production practices, there are often competing side reactions or reaction chains proceeding rapidly in parallel with the targeted reaction. These reactions, happening among products, intermediates and raw materials, are directly influenced by the reaction progress and the components' concentration distribution in the reaction system. Therefore, the primary mixing of materials is of great importance for the distribution, yield and quality of the targeted products and has strong impact on the designs and energy efficiencies of the overall production processes.
Taking syntheses of isocyanates (e.g., MDI or TDI) for example, the processes are mainly composed of phosgenations at ambient and elevated temperatures. After dissolution of liquid polyamines and liquid phosgene in inert solvents such as chlorobenzene, toluene, dichlorobenzene, chloro-naphthalenes, 1,2,4-trichlorobenzenes, etc., the reaction at ambient temperature takes place at 0 to 90° C. and mainly forms amides and polyamine hydrochlorides as well as a small amount of urea. The principal reactions are as follows:RNH2+COCl2→RNHCOCl+HCl  (1)RNH2+HCl→RNH2.HCl  (2)RNH2+RNHCOCl→RNCO+RNH2.HCl  (3)RNH2+RNCO→RNHCONHR  (4)
At the stage of phosgenation at ambient temperature, polyamines firstly react with phosgene to yield carbamoyl chloride, i.e. Reaction (1), this is a rapid exothermic reaction which proceeds to completion instantaneously; simultaneously, HCl resulting from Reaction (1) reacts with the polyamines rapidly, i.e. Reaction (2), to yield polyamine hydrochloride. Both carbamoyl chloride and polyamine hydrochloride are solids that are insoluble in the reaction system. When the local mixing effect of phosgene and polyamine is relatively poor, excessive polyamines in this area will react with carbamoyl chloride or isocyanate, as shown in Reactions (3) and (4) respectively, yielding urea as an unwanted by-product which is viscous and insoluble in the reaction system. This process exhibits complicated serial competitive reactions. The principal reaction is an instantaneous reaction that completes in milliseconds or even faster, the product of which further reacts with the raw materials rapidly, yielding by-products insoluble in the reaction system. Therefore, the initial mixing of the two raw materials directly decides the yield and selectivity of the target product. To design a high-speed liquid mixing reactor that improves the initial mixing of the two raw material streams, is of great significance for increasing the yield and selectivity of the target product and reducing the viscous by-product.
For another example, the reaction between aniline and formaldehyde to produce polymethylene polyphenylene polyamine, mainly comprises reaction stages including salt-formation, pre-condensation and the rearrangement. In the pre-condensation reaction stage, a liquid mixture of aniline hydrochloride and the circulated liquid is brought into rapid contact with formaldehyde to perform the pre-condensation reaction at a temperature ranging from 20 to 90° C.; a better microscopic dispersion of formaldehyde is beneficial for the results of the reaction. Excessive formaldehyde in local area results in the formation of macromolecular products and more impurities. If formaldehyde is locally over-excessive, there will be web-like polymers generated, which are insoluble and prone to clog up the equipment, and will consequently affect the operation. Therefore, the initial mixing of the two raw materials directly decides the yield and selectivity of the target product. To design a high-speed liquid mixing reactor that improves the initial mixing of the two raw material streams, is of great significance for increasing the yield and selectivity of the target product and reducing the viscous by-product.
The cross-flow mixing is an important technique to achieve rapid mixing of fluids, which can be achieved in one way by jetting one fluid stream via a plurality of apertures into another fluid stream. The jetted stream is split in a plurality of fine steams by the apertures. When jetted into the main stream of the other fluid, each fine stream is rapidly wrapped by the main stream, thereby achieving a rapid mixing of the two streams of fluids.
U.S. Pat. No. 5,117,048 disclosed a hole-jetting reactor (as shown in FIG. 1), which enabled rapid mixing of two streams of fluids by cross flow, jetting one stream (polyamine) into the main stream (phosgene) via apertures evenly distributed over a neck portion. This reactor increased the intensity of turbulence in these two streams of materials mainly by the design of neck portion, so as to improve the initial mixing of the materials. This reactor design allowed reducing the amount of solvent for dilution of the reactants.
U.S. Pat. No. 5,931,579 disclosed a reactor which realized mixing by using a rotator and a stator to engage each other (see FIG. 2). Two fluid streams were fed in between the rotator and the stator and the mixing was driven by the rotation of the rotator. The rotation of the rotator intensified the turbulence and realized the rapid mixing of the two streams of fluids, which reduced the amount of solvent for dilution.
The exemplification above shows that the initial mixing of the two streams of feeds in a well-distributed way is very important. The rapid mixing of streams may be realized to some extent either by using a hole-jetting type reactor which jets a fluid stream into another stream at a high speed or by using a stirring type reactor which feeds two fluid streams into a stirring zone of the rotator. As fluids have thickness, space and turbulence zone are essential to achieve sufficient mix-up. The mixing of two fluids is relatively easier when the fluids have lower flow rates. However, large scale production activities require larger flow channels, which may result in poor distribution and mixing of two streams of feeds in a short time. An extra distance is necessary to achieve the mixing effect but may increase the possibility of side reactions. Both the two types of reactors as discussed above have a capacity limit and a degraded reaction effect under a high workload, and thus it is necessary to develop a high-speed mixing apparatus with better mixing effect to achieve a rapid mixing-reaction of feeds under a massive capacity of production.